The present invention relates to a flat image display device including apparatus for scanning electron beams over the image screen thereof, and particularly to a structure for confining and guiding the beams and for selectiely deflecting the beams toward the image screen.
It has long been a desire to reduce the depth dimension of a picture tube to provide a substantially flat display device. One structure which has been proposed includes a thin boxlike envelope with one of the large sides thereof constituting a faceplate on which a phosphor screen is disposed. An electron gun directs electrons across the tube in a path substantially parallel to the screen. Deflection elements are provided to selectively deflect the electrons onto successive points of the screen to achieve the desired scanning thereof. A tube of this type is shown in U.S. Pat. No. 2,928,014 to W. R. Aiken et al, issued Mar. 8, 1960 entitled "Electronic Device Cathode Ray Tubes".
In using this technique a problem has arisen in making flat display devices having large area screens, such as screens which are about 75 centimeters by 100 centimeters. For large size devices some type of internal support structure is required to prevent the evacuated tube from collapsing. A device having such internal support is shown in U.S. Pat. No. 2,858,464 to W. L. Roberts, issued Oct. 28, 1958, entitled "Cathode Ray Tube". In a tube having internal structure, the confinement and guiding of the electron beam is more critical to prevent the supporting structure from interfering with the electron beam. As a beam of electrons moves away from its source, the electrons tend to spread out, making the size of the beam larger. If the electrons spread out enough to contact the supporting structure, parts of the tube become charged and cause malfunctioning of the tube.
As described in the copendng application of T. O. Stanley, Ser. No. 607,492, filed Aug. 25, 1975, entitled "Flat Electron Beam Addressed Device" the confinement of the electron beam can be accomplished by means of beam guides which apply electrostatic forces to the electrons of the beam to confine the electrons in a relatively small beam as the beam travels along a path across the envelope. The beam guide also provides for deflection of the beam out of its path toward the phosphor screen at selective points along the beam path. For ease of construction of such a flat display device, it is desirable that the beam guides be of a relatively simple construction, i.e., the guide be made up of a minimum number of parts which can be easily assembled, yet still perform its desired function.